How to Identify if Brake Discs are worn?

[Arnie91]

I purchased a new Merc couple of days ago.

The rear has a slicing sound coming from the brake disc or pad which we initially thought would go away once the rust had come off. It now looks as if the brake discs are really worn, there's a lot of chipping on the outside of the brake disc and rust.

Anyone have any pictures or guides as to how to identify how worn a disc is?

 

[PobodY]

Isn't it normally done by measuring the thickness? Once it has lost enough, it's toast and needs to be replaced.

If it's still got meat, then you might be able to get it resurfaced... but it might be just as cost effective to replace them (especially if they're chipped as described).

 

[GordonTarling]

There'll be a minimum thickness quoted either by the disc manufacturer or Mercedes. In my experience, cars bought from dealers often suffer from corroded discs due to the fact that they sit around for weeks/months on forecourts without being driven. You've just bought the car, so if you bought it from a dealer, they are obliged to fix it.

 

[Arnie91]

Yeah they've said any issues I find they will fix it.

I'm taking it to Wayne Gates in Harrow for a post purchase inspection. Hopefully they dig out everything. The dealer was Car Giant and I have it in recording that the car was supposed to be sold without absolutely any issues.

Car Giant workshop inspection next Wednesday for Brake checks and any potential issues they said they'll get the parts in it and change it free of cost.

Going to push for new discs all round.

 

[Benzowner]

Rear brakes are used very lightly in normal running, most braking is done by the fronts, not sure of the figure but I think it's about 70/30 front to rear, so unless you brake heavily, the rears will be used very little.

 

[Arnie91]

There's a sort of slicing/grinding sound on the rears even when im not breaking and just rolling along. On the Rear right side. Maybe the issue isn't to do with the brake discs but the pads being too close?

 

[whitenemesis]

Or it might be a badly adjusted parking brake on that side?

 

[Deleted member 131833]

Is the car automatic? I have trouble with handbrake on my cars seizing due to not being used as I used the transmission lock instead.

Depress hand (foot) brake and release a few times and see if that stops the grinding at the rear

 

[wu56Shoozz]

On the Brembo Disc there is a dimple on the surface of it ... if its not there then its toast.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

How to Check Disc Brakes - dummies

How to Identify Badly Worn Brake Discs - Google Search

 

[Yugguy]

Is the car automatic? I have trouble with handbrake on my cars seizing due to not being used as I used the transmission lock instead.

Depress hand (foot) brake and release a few times and see if that stops the grinding at the rear

Ever thought of making the problem go away by actually using it?

I know it's a daft implementation with a foot pedal and a hand flap but I've just got into the habit of using it.

Saves worry on MOT day too as a functioning parking brake is needed to pass.

 

[MancMike]

If it looks like this, it's worn.

 

[Deleted member 131833]

Ever thought of making the problem go away by actually using it?

Nope! Cannot be bothered with it

 

[Arnie91]

Yeah it's automatic,

I didnt know there was a rear parking brake. New to these cars but I have experience working on an A4 1.8T, but this is something completely different.

 

[whitenemesis]

Even automatics have to have a parking brake.

The parking brake drum is part of the rear service brake disc,

 

[wu56Shoozz]

If it looks like this, it's worn.

Do you guys know nothing about cars..

That's them new Grooved discs from India by manufacturer Brakeadoof.. really good on older cars I'm told, Like Austins & Bel (Ends) Airs etc....

 

[190]

My best grinding noise on a brake disk was caused by the brake pad material shearing off the back plate - at 7pm on a Sunday night 200 miles from home and towing a trailer and it wasn't a braked trailer. Could have been worse I suppose. I made it home using the hand brake and a lot of engine braking. The brakes still worked if I needed them in an emergency but the noise of steel on steel didn't encourage it. Reckless perhaps but there was very little traffic on a Sunday night in the 70's.

 

[PobodY]

I've run a set of pads down to the metal before (when I was a student in the mid '90s) and just had to take it really gently until I could limp it in to a mechanic. - There's still braking force on the other wheels, but it's not as much as you're expecting.

 

[brucemillar]

Some left foot braking may clean the disc surfaces. This may just be some rust 'run out' that requires cleaning off. Find a quiet stretch of road, drive down it at 30mph + and brake with your left foot whilst maintaining throttle position with the right foot. Do this in several 3 second bursts (having checked your mirrors first please). YOu do need enugh pressure on the left foot for the car to slow against the throttle.